1. Field of the Invention
This invention relates to a foamable thermoplastic clastomer composition and method of producing the same, more particularly to a foamable thermoplastic elastomer composition containing thermally expandable microcapsules and a method of producing the same.
2. Description of the Prior Art
Recently, resins have been foamed for improving their properties, e.g., heat insulation, sound insulation and shock absorption, and reducing their weight. The foamed resins are widely used for various purposes, e.g., gaskets for construction materials, floor materials, piping protection materials, shoe soles, door packings, sporting goods, grips, toys, vibration insulators, heat insulators, sound insulators and shock absorbers.
One method of producing the foamed resins includes a foaming agent in ethylene-xcex1-olefin-based copolymer rubber to produce a thermoplastic hollow resin, as disclosed by Japanese Patent Laid-open Publication No. S59-1541. The method of foaming the above resin uses a foaming agent, e.g., nitroso, azo or urea compound. Use of these foaming agents, however, causes several problems, e.g., unstable foamed conditions, uneven size of the cells, and difficulty in continuously producing formed articles of foamed resins.
Japanese Patent Laid-open Publication No. S59-196328 discloses a rubber composition for foaming, composed of rubber or rubber elastomer incorporated with microcapsules, wherein the capsule shell of a thermoplastic resin contains core material which can expand the shell when heated. Moreover, Japanese Patent Laid-open Publication No. H4-246440 discloses a rubber composition composed of a rubber-like polymer incorporated with heat-expandable microcapsules starting to expand at 120xc2x0 C. or higher, wherein the capsule shell of an acrylonitrile copolymer contains a low-boiling point hydrocarbon. Even these methods which use heat-expandable microcapsules cannot stabilize the foamed conditions, and it is difficult to cause the resin to have uniformly sized cells that are continuously formed in the expanded article. Another problem is the forming method is limited to pressing, when a vulcanized rubber material is used.
It is an object of the present invention to provide a foamable thermoplastic elastomer composition which can be formed into a stable foamed article incorporated with heat-expandable microcapsules, in consideration of the above problems. It is another object of the present invention to provide a method of producing the same.
The inventors of the present invention have found, after having extensively studied to solve the above problems, that a foamable thermoplastic elastomer composition which can be formed into stable foamed articles can be obtained by incorporating a thermoplastic resin with a resin composition containing an olefin-based resin having a specific melting or softening point, heat-expandable microcapsules which expand at 120 to 300xc2x0 C. and the volatile composition. In particular, the inventors have found that the stable elastomer composition for foamed articles is obtained by kneading the composition in two stages at a specific temperature or lower, thereby achieving the present invention.
The first aspect of the invention is a foamable thermoplastic elastomer composition which contains:
(a) 10 to 90 parts by weight of one of an olefin-based resin and rubber having a melting or softening point of 140xc2x0 C. or lower;
(b) 9 to 85 parts by weight of heat-expandable microcapsules expanding at 120 to 300xc2x0 C.; and
(c) 1 to 50 parts by weight of a volatile composition,
wherein the components (a) to (c) total 100 parts by weight.
The second aspect of the invention is a foamable thermoplastic elastomer composition which contains:
(a) 10 to 90 parts by weight of one of an olefin-based resin and rubber having a melting or softening point of 140xc2x0 C. or lower;
(b) 9 to 85 parts by weight of heat-expandable microcapsules expanding at 120 to 300xc2x0 C.;
(c) 1 to 50 parts by weight of a volatile composition; and
(d) 50 to 99 parts by weight of a thermoplastic resin, wherein the components (a) to (d) total 100 parts by weight.
The third aspect of the invention is the foamable thermoplastic elastomer composition of the first or second aspect, wherein said volatile composition (c) has a boiling point of 90 to 250xc2x0 C., or evaporates at (0.5 g/1000 cm2)/hour or more at 100xc2x0 C.
The fourth aspect of the invention is the foamable thermoplastic elastomer composition of the first or second aspect, wherein said volatile composition (c) is of at least one type selected from the group consisting of a hydrocarbon and oxygen-containing compound.
The fifth aspect of the invention is the foamable thermoplastic elastomer composition of the first or second aspect, wherein said volatile composition (c) is of at least one type selected from the group consisting of water and water-containing composition, and contained at 1 to 30 parts by weight per 100 parts by weight of the components (a) to (c) totaled.
The sixth aspect of the invention is a method of producing a foamable thermoplastic elastomer composition by kneading, at 140xc2x0 C. or lower, (a) 10 to 90 parts by weight of one of an olefin-based resin and rubber having a melting or softening point of 140xc2x0 C. or lower, (b) 9 to 85 parts by weight of heat-expandable microcapsules expanding at 120 to 300xc2x0 C., and (c) 1 to 50 parts by weight of a volatile composition.
The seventh aspect of the invention is a method of producing a foamable thermoplastic elastomer composition, wherein the composition is produced in two stages, the first stage kneading, at 140xc2x0 C. or lower, (a) 10 to 90 parts by weight of one of an olefin-based resin and rubber having a melting or softening point of 140xc2x0 C. or lower, (b) 9 to 85 parts by weight of heat-expandable microcapsules expanding at 120 to 300xc2x0 C., and (c) 1 to 50 parts by weight of a volatile composition, to produce the resin composition containing the components (a) to (c), and the second stage adding the resin composition containing the components (a) to (c) to (d) a thermoplastic resin, and kneading these components.
The eighth aspect of the invention is the method of the seventh aspect for producing a foamable thermoplastic elastomer composition, wherein the ratio of said resin composition containing the components (a) to (c)/thermoplastic resin (d) is any weight ratio from 1.0:99.0 to 50:50.
The ninth aspect of the invention is the method of the sixth or seventh aspect for producing a foamable thermoplastic elastomer composition, wherein said volatile composition (c) has a boiling point of 90 to 250xc2x0 C., or evaporates at (0.5 g/1000 cm2)/hour or more at 100xc2x0 C.
The tenth aspect of the invention is the method of the sixth or seventh aspect for producing a foamable thermoplastic elastomer composition, wherein said volatile composition (c) is of at least one type selected from the group consisting of a hydrocarbon and oxygen-containing compound.
The 11th aspect of the invention is the method of the sixth or seventh aspect for producing a foamable thermoplastic elastomer composition, wherein said volatile composition (c) is of at least one type selected from the group consisting of water and water-containing composition, and contained at 1 to 30 parts by weight per 100 parts by weight of the components (a) to (c) totaled.
The 12th aspect of the invention is the method of the sixth or seventh aspect for producing a foamable thermoplastic elastomer composition, wherein a kneader is used for kneading the components.
The foamable thermoplastic elastomer composition of the present invention is described in more detail with respect to its components, method of production and purposes.
1. Components of the Expandable Thermoplastic Elastomer Composition
(1) Olefin-based Resin or Rubber Component (a)
The olefin-based resin or rubber component (a) for the present invention includes olefin-based copolymer rubber and amorphous polyolefin. The olefin-based resin or rubber has a melting or softening point of 140xc2x0 C. or lower. The melting or softening point exceeding 140xc2x0 C. may cause problems, e.g., undesirous expansion of the heat-expandable microcapsules or evaporation of the volatile composition during the kneading step, and decreased expansion ratio when incorporated in the component (d). The component (a) may be composed of one or more types of olefin-based resin or rubber.
The olefin-based copolymer rubber usexcex1ful for the component (a) includes an elastomer of copolymer of xcex1-olefin, e.g., ethylene, propylene, 1-butene or 1-pentene, and olefin-based rubber of copolymer of an xcex1-olefin and non-conjugated diene. The non-conjugated dienes useful for the present invention include dicyclopentadiene, 1,4-hexadiene, dicyclooctadiene, methylenenorbornene and 5-ethylidene-2-norbornene or the like.
More specifically, these olefin-based copolymer rubbers include ethylene/propylene, ethylene/propylene/non-conjugated diene, ethylene/1-butene, ethylene/1-butene/non-conjugated diene, and ethylene/propylene/1-butene copolymer rubbers or the like.
The amorphous polyolefin useful for the present invention is composed of an amorphous copolymer mainly comprising propylene and having a melt viscosity of 250 to 50,000 mPaxc2x7s at 190xc2x0 C. preferably 10,000xcx9c25,000 mPaxc2x7s at 190xc2x0 C. It is a polymer of relatively low molecular weight, having a crystallinity degree of 50% or less, determined by X-ray diffractometry, preferably 20% or less. It preferably has a glass transition temperature of xe2x88x9233 to xe2x88x9223xc2x0 C., and softening point of 120 to 135xc2x0 C.
More specifically, the amorphous polyolefins useful for the present invention include atactic polypropylene as an amorphous homopolymer, and propylene-based amorphous copolymers with another xcex1-olefin (e.g., ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene or 1-decene). Of these amorphous polyolefins, atactic polypropylene amorphous homopolymer, propylene/ethylene amorphous copolymer and propylene/1-butene amorphous copolymers are preferable. These amorphous polyolefins may be random or block copolymers. In the case of the block copolymer, its propylene unit should be bonded to have the atactic structure. In the case of the copolymer of propylene and ethylene, the propylene unit content is preferably at least 50% by mol, more preferably 60 to 100% by mol.
Content of the component (a) is 10 to 90 parts by weight, preferably 15 to 70 parts by weight, more preferably 20 to 60 parts by weight, wherein the components (a) to (c) total 100 parts by weight. At a content below 10 parts by weight, the resin composition may have insufficient properties, e.g., strength, and be difficult to knead. Moreover, uniform dispersion or foaming may not be reliable. At above 90 parts by weight, on the other hand, the resin composition may not foam to the required extent, because of difficulty in effecting the sufficient expansion effect.
(2) Heat-expandable Microcapsule Component (b)
The heat-expandable microcapsule component (b) of the present invention has the effect of increasing volume and decreasing specific gravity by thermal expansion. It thermally expands at 120 to 300xc2x0 C., preferably 140 to 260xc2x0 C. When the thermal expansion temperature is below 120xc2x0 C., the thermoplastic elastomer composition may undesirably expand under heating while being prepared, and have deteriorated resistance to heat. When it is above 300xc2x0 C., on the other hand, the thermoplastic elastomer composition may not thermally expand in the forming or fabrication temperature range.
The heat-expandable microcapsule expanding at 120 to 300xc2x0 C. should have an average particle size of 1 to 50 xcexcm. If its average particle size is below 1 xcexcm, it may not be sufficiently dispersed in the rubber. When it is above 50 xcexcm, on the other hand, the formed article of the composition of the present invention will have greatly reduced strength. Its expansion ratio is preferably 10 to 100. At a ratio below 10, the microcapsule may not sufficiently expand. At a ratio above 100, on the other hand, uniformly fine cells may not be obtained. One example of the heat-expandable microcapsules is Expancel (supplied by Expancel Co.) with isobutane contained by the outer shell of vinylidene chloride/acrylonitrile copolymer.
Content of component (b) is 9 to 85 parts by weight, preferably 15 to 70 parts, more preferably 20 to 60 parts by weight, wherein the components (a) to (c) total 100 parts by weight. At a content below 9 parts by weight, the characteristics of the resin composition will be largely determined by those of the base resin, because of insufficient expansion effect. At above 85 parts by weight, on the other hand, the resin composition may not be well kneaded, causing reduced cell uniformity.
(3) Volatile Composition Component (c)
The volatile composition component (c) of the present invention causes the elastomer composition to foam. As a result, the composition is stably foamed due to the effect of the component (c) increasing the volume and decreasing the specific gravity of the composition. The volatile composition is composed of hydrocarbons, oxygen-containing compounds, water, water-containing composition or the like which has a boiling point of 90 to 250xc2x0 C. or evaporates at (0.5 g/1000 cm2)/hour or more at 100xc2x0 C.
The volatile composition will excessively lose its volatiles by evaporation during the kneading step, when its boiling point is below 90xc2x0 C. When it is above 250xc2x0 C., on the other hand, the composition will no longer work as the foaming aid for the heat-expandable microcapsules as component (b), because the volatiles cannot evaporate sufficiently during the forming or fabrication step to bring about the effect of expanding the elastomer composition. Moreover, the volatile composition evaporating at below (0.5 g/1000 cm2)/hour may no longer work as the foaming aid, because of insufficient foaming effect during the forming or fabrication step.
The evaporation rate at 100xc2x0 C. may be determined by a halogen moisturemeter HG53 (METTLER-TOLEDO Co.). For example, an adequate quantity (20 g) of the sample solution, put in a drip tray (70 cm2), is heated to 100xc2x0 C. in around 60 seconds, at which it is held for a constant time (10 minutes) at constant intervals (1 minute), to determine water content by the following formula:
Water content=(Weight after the testxe2x88x92Weight before the test)xc3x97100/Weight before the test 
In the case of H2O, for example, the evaporation rate is (99 g/1000 cm2)/hour.
The specific examples of the volatile compositions having a boiling point of 90 to 250xc2x0 C. include hydrocarbons, e.g., heptane, ligroin, methyl cyclohexane and non-aromatic-based oil having a specific gravity of 0.83 or less; and oxygen-containing compounds, such as alcohols (e.g., n-propyl alcohol, isobutyl alcohol and phenols), ethers (e.g., dioxane), fatty acids (e.g., acetic acid), fatty acid esters (e.g., sec-butyl acetate and ethyl propionate), ketones (e.g., acetal and methylisobutylketone), and diacid esters (dibutyl adipate, dibutyl sebacate, dimethyl acetylricinoleate and dibutyl acetylricinoleate).
The volatile compositions having an evaporation rate of (0.5 g/1000 cm2)/hour or more at 100xc2x0 C. include 2,2,4-trimethyl-1,3-pentanediol diisobutyrate and 1,5-dihydroxy pentane. These compositions are commercially available, e.g., xe2x80x9cNeothiosolxe2x80x9d (Sanko Chemical Industries Co.) and xe2x80x9cTXIBxe2x80x9d (Eastman Chemical Co.).
The water-containing compositions useful for the present invention include silica sol, where the negative-charged silica particles repel each other because the silanol groups on the silica particle surfaces are bound to the hydroxyl ions in an alkaline condition, to be stably present without being bound to each other. Sodium or ammonium hydroxide is used as the alkalization agent. The silica particles are amorphous, highly dense and pure, and spherical, having a density of 2.1 to 2.2 g/cm3 and particle size of 10 to 20 xcexcm. When dried, silica sol has hydroxyl group on the surface dehydrated to release water. These silica sols are commercially available, e.g., xe2x80x9cAdelite ATxe2x80x9d (Asahi Denka Kogyo Co.).
The content of component (c) is 1 to 50 parts by weight, preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, wherein the components (a) to (c) total 100 parts by weight. When the component (c) is of at least one type selected from the group consisting of water and water-containing composition, the content is 1 to 30 parts by weight, preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight. At a content of component (c) below 1 part by weight, the resin composition may have the effect of insufficient expansion, and its characteristics will be essentially determined by those of Expancel. At above 50 parts by weight, on the other hand, the resin composition may not be kneaded well and thereby lose cell uniformity. At a concentration of the component (c) above 30 parts by weight, when it is of at least one type selected from the group consisting of water and water-containing Composition, the resin composition may not be kneaded well and thereby lose cell uniformity.
(4) Thermoplastic Resin Component (d)
The thermoplastic resins useful as component (d) of the present invention include polyolefin-based resins (e.g., polypropylene, propylene/ethylene copolymer, propylene/butene copolymer, polyethylene, ethylene/vinyl acetate copolymer, ethylene/acrylate copolymer, ethylene/acrylic acid copolymer, and ionomer), cyclic hydrocarbon-based resins (e.g., cyclic olefin copolymer), polystyrene-based resins (e.g., polystyrene resin, acrylonitrile/styrene copolymer (AS resin), acrylonitrile/butadiene/styrene copolymer (ABS resin), methacrylate/styrene copolymer (MS resin), methacrylate/butadiene/styrene copolymer (MBS resin), styrene/maleic anhydride copolymer (SMA resin), styrene/conjugated diene copolymer, and hydrogenated compounds of these copolymers (SBS, SIS, SEBS, SEPS and SBBS)), styrene-based elastomer compositions (e.g., compositions composed of at least one type selected from the group consisting of styrene/conjugated diene copolymer and hydrogenated compound thereof, non-aromatic-based softening agent for rubber, and polyolefin-based resin), polyamide-based resins (e.g., polyamide and polyamide-based elastomer), polyester-based resins (e.g., polyester and polyester-based elastomer), polyurethane-based resins (e.g., polyurethane and polyurethane-based elastomer), polyvinyl-based resins, and polycarbonate-based resins. Of these, olefin- and styrene-based resins are more preferable, and styrene-based elastomer compositions are still more preferable.
The content of the component (d) is 50 to 99 parts by weight, wherein the components (a) to (d) total 100 parts by weight. In other words, the ratio of the resin composition containing the components (a) to (c) to the thermoplastic resin (d) is any weight ratio from 1.0:99.0 to 50:50, preferably 3:97 to 35:65, more preferably 5:95 to 30:70.
(5) Other Components
The foamable thermoplastic elastomer composition of the present invention may be incorporated with other optional components, as desired, within limits not adverse to the object of the present invention. These optional components include a plasticizer, softening agent, inorganic filler, blocking inhibitor, sealing improver, heat stabilizer, antioxidant, light stabilizer, ultraviolet ray absorber, lubricant, nucleating agent and colorant or the like.
The antioxidants useful for the present invention include phenol-based ones, e.g., 2,6-di-tert-p-butyl-p-cresol, 2,6-di-tert-butyl phenol, 2,4-dimethyl-6-tert-butyl phenol, 4,4-dihydroxydiphenyl and tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane; phosphate-based ones; and thioether-based ones. Of these, phenol- and phosphate-based ones are particularly preferable.
The plasticizers and softening agents useful for the present invention include phthalate ester-based plasticizers, aromatic carboxylate-based plasticizers, aliphatic dibasic acid ester-based plasticizers, phosphate ester-based plasticizers, polyester-based plasticizers, epoxy-based plasticizers, and non-aromatic-based softening agents for rubber. They may be used either individually or in combination. More specifically, these plasticizers include di-normal butyl phthalate (DBP), di-2-ethylhexyl phthalate (DOP), diisooctyl phthalate (DIOP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), diisobutyl adipate (DIBA), di-2-ethylhexyl adipate (DOA), diisooctyl adipate (DIOA), diisodecyl adipate (DIDA), di-normal butyl sebacate (DBS), dialphanol sebacate (DAS), di-secondary butyl azelate (DOZ), di-isooctyl azelate (DIOZ), tri-2-ethylhexyl phosphate (TOP), tricresyl phosphate (TCP) and trixylenyl phosphate (TXP) or the like. The non-aromatic-based softening agent for rubber is a non-aromatic-based mineral oil, or liquid or low-molecular-weight synthetic agent. The softening agents of mineral oil for rubber are generally a mixture of an aromatic ring, naphthenic ring and paraffin chain. They are distinguished from each other by the paraffin-, naphthene- and aromatic-based ones, when carbons in the paraffin chains account for 50% or more of the total carbons, those in the naphthene rings for 30 to 40%, and the aromatic ones for 30% or more, respectively. The paraffin- and naphthene-based ones, defined above, are preferable for the mineral oil-based softening agent for rubber as the optional component for the present invention, and paraffin-based one is more preferable. Moreover, the paraffin-based one having a lower aromatic ring content is more preferable. The non-aromatic-based softening agent for rubber preferably has a kinematic viscosity of 20 to 500 cst at 37.8xc2x0 C., pour point of xe2x88x9210 to xe2x88x9215xc2x0 C., and flash point (COC) of 170 to 300xc2x0 C.
2. Method of Producing the Expandable Thermoplastic Elastomer Composition
The foamable thermoplastic elastomer composition of the present invention can be produced by kneading the above-described components of the specified content by a kneading machine, e.g., roll, kneader, Banbury mixer, single-screw extruder, twin-screw extruder or multi-screw extruder. A kneader and Banbury mixer are preferable, and a combination of kneader and extruder is more preferable. It is preferable to continuously extrude the starting mixture supplied batchwise.
The foamable thermoplastic elastomer composition of the present invention is produced in two stages: the first stage involves kneading the components (a) to (c) at a specified content to obtain the resin composition, and the second stage involves adding the resin composition prepared in the first stage to the component (d) of specified content.
The methods of kneading components (a) to (c) at a specified content in the first stage include the followings: p1 (i) blending the components (a) to (c) in a lump, and kneading the mixture by a kneading machine also in a lump,
(ii) melting the component (a), to which the components (b) and (c) are added, and kneading these components, and
(iii) mixing the component (a) with the component (c) and then with the component (b), and kneading these components.
Of these methods, the methods (i) and (ii) are more preferable. The melting/kneading temperature is 140xc2x0 C. or lower, preferably 120xc2x0 C. or lower. At above 140xc2x0 C., the heat-expandable microcapsules as the component (b) partially expand to release some of the volatiles into the air, decreasing the expansion ratio when incorporated in a thermoplastic resin as the component (d). The method (i) or (ii) gives the thermoplastic elastomer composition excellent in thermal expansion, because of reduced exposure of the heat-expandable microcapsules as the component (b) and volatile composition as the component (c) to heat.
The foamable thermoplastic elastomer composition of the present invention, being excellent in thermal expansion and formability/fabricability, can be expanded into a stable thermoplastic elastomer. It is more stable in closed cell structure, more uniform in cell size, and at least 2 times higher in expansion ratio than the one prepared by individually applied water-aided, chemical or thermal expansion.
Therefore, the foam of the foamable thermoplastic elastomer composition of the present invention is excellent in that it is light, and it is also excellent in its vibration-damping, vibration-insulating, sound-insulating and elasticity-recovering properties, and, as such, is suitable, for example, as various types of sealants, and vibration-damping and vibration-insulating parts for various areas, e.g., automobiles, home electric appliances, construction and IT-related industries.